Yes they will. No client would pay me to kill someone and not expect to see evidence of the murder. The evidence (usually in a photo) would reveal how the target died.
The evidence (usually in a photo) would reveal how the target died.
The problem is photos can be faked.
There was this case where a guy called Dread Pirate Roberts, the admin of a site called Silk Road (a website that was selling drug online before getting shut down once by the feds) ordered a hit on one of his lieutenants which was, unbeknownst to him, working for the feds. So the feds faked his murder and staged a murder scene with the snitch playing the role of his own corpse, photographed the whole shebang as a proof of 'execution' and then charged Roberts with conspiracy to commit murder.
Have a read at this article:
http://arstechnica.com/tech-policy/2013/11/target-of-silk-road-murder-for-hire-plot-tells-his-story/
Apparently blood starts to decompose fast after death and is different than blood taken from a living person (but then again I'm no doctor) maybe a syringe of blood could be a better 'proof of death'.
Or a vital organ but that's messy and could tie the killer directly to the crime scene which is good if the client is the receiver of the organ but bad if the cops discover it.
I would not want to use someone's organ as proof. It's too messy. And a syringe of blood wouldn't prove anything, as it could be taken from anyone. The client is not exactly going to test the blood himself to prove where it came from. Though, some might if they were paranoid enough and had access to a lab.
Video footage is another way to prove the murder took place, as long as it's completely destroyed afterwards.
Anyway the fact that the target has disappeared or that his body has turned up dead somewhere could be proof enough because that's all the client is asking for.
Plus an experienced assassin would have his/her body of work (semi-intentional pun) talking for themselves.
One problem that I see is how to advertise a murder-for-hire service. Plus all the small details like having a day job as a front, having access to hidden bank accounts to get paid.
Knowing an expert at fabricating documents and IDs would be almost mandatory too in order to circulate freely.
Access to weapons and the knowledge needed to dispose of them without a trace.
Being physically inconspicuous in order to blend in is also necessary.